Few shots with recent status;
I have covered hull with some 3d print resin; it should make it watertight and smooth surfaces. I plan to slightly sand it now; than apply base and final coating.
I have also created some 3d printed water inlets which I have installed in bottom and supported from inner bottom. Also I have drilled a whole through transom and glued inside copper pipes for cooling outlet. All propulsion is printed and set together. I’m using here modified version of shaft with bigger hex size. Looks like we can soon see her on the water 🙂

Some problems I have experienced:
1. Printing of windshield appeared to be somehow challenging; I’m struggling to achieve smooth surface due to inner structure inside it.
2. Rubber sealing; bow part appeared to be challenging; it took me 4x to have finally good effect; speed was reduced to 25% of originals, temperature for filament was important factor which you have to find yourself for material you own.

That is mine concern too, my boat is soon to be launched. Completing mechanical elements together I have noticed that bearings are generally moving quite easy on shaft. I think this could be glued on some sanitary silicone?

Regarding rudder printing; I had issues with nozzle height above printing bed; if it is too low it is basically melting whole 1st layer into one object. Type of material matetrs as well, it is little more difficult with PET-G but I finally managed.

Regarding jet idea; description is saying about boats up to 1m of length – I think it should be enough, there are in general two options:
1. Single jet propeller in the middle, example I have sent you is about it, it is also shaped to similar angle like your boat. This project included steerable vector of trust but no reverse. Modification would have to flash bottom of the boat and include channel for jet propulsion. I would also propose to add already a cooling inlet and outlet.
2. Two jet propellers on sides. Than we don’t need steerable trust vector but we could include reverse trust option. Should still provide good maneuverability. Modifications of hull would have to flash whole last segment of bottom and include 2 channels for jet propulsion and engines foundation. Also inlets and outlets for cooling would have to be added.

IMO this will not change anything; still weakest part will be HEX cross section; there is v2 of shaft available which have this part increased to max of other elements – I suggest to use screw which is shorter – 12mm?

Actually back wheel is pressing fwd 🙂 Problematic is proposed size of screw – it is too long, when you use force you are breaking thread in plastic of shaft and whole thing is much more fragile.
I have also tested shaft with bigger HEX part but this is about real torque transmission.

Ulf… woudl you be interested in cooperation to make a version with jet propulsion? Something like this? JET